JPS62239198A - Voice reproduction circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

TECHNICAL FIELD The present invention relates to an audio reproducing circuit, and more particularly to an audio reproducing circuit that reproduces a plurality of audio information.

BACKGROUND ART Conventionally, when mixing a plurality of digital audio waveforms, this type of audio playback circuit has conventionally used a digital audio waveform output circuit 1-1 (i=1...) as shown in FIG.
, n) are respectively D/A converted by a D/A (digital analog) converter 6-1,
The signals are passed through an LPF (low-pass filter) 7-1 and converted into analog audio signals, which are then input to an adder 8 for mixing.

The adder 8 is composed of an operational amplifier and the like.

If this mixing was performed using a linear D/A converter 5-i, only the adder 8 would be required, but recently nonlinear D/A converters (for example, μ-law) are often used for the purpose of cost reduction. In this case, the data must be linearly transformed and then added, which is a large-scale process.

Such a conventional audio reproduction circuit has a configuration in which multiple digital audio waveforms are individually D/A converted and passed through the LPF 7-i, which is expensive.
Since F7-i is required as many as the number of audio signal circuits,
The disadvantage is that the larger the number of circuits, the larger the device size.

Also, when mixing multiple digital audio waveforms,
Since mixing was done using an analog audio waveform, there was a drawback that noise easily entered the analog waveform, and noise was superimposed by the number of mixing circuits.

OBJECTS OF THE INVENTION The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional circuit, and therefore, it is an object of the present invention to provide an audio reproduction circuit that is inexpensive, can be made small in size, and is less susceptible to noise.

An audio reproduction circuit according to the present invention is an audio reproduction circuit that mixes and reproduces a plurality of pieces of audio information, and includes a multiplexing means for multiplexing each of the audio information as a digital signal. The present invention is characterized in that the output of the converting means is reproduced into an analog signal.

Embodiment Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In the figure, in this embodiment, a digital audio waveform output circuit 1
-i A multiplexing circuit 2 that multiplexes digital audio waveforms from (i-1,..., n) in a time division manner, and a multiplexing circuit 2 that multiplexes the digital audio waveforms from the multiplexing circuit 2 at a sampling frequency. It is composed of a D/A converter 3 that performs D/A conversion at several times the frequency, and an LPF 4 that passes only signal components output from the D/A converter 3 whose frequency is approximately half the sampling frequency or less. There is.

FIG. 2 is a time chart of the multiplexing circuit 2, and this figure describes the case where there are two digital audio waveform output circuits 1-1.

In the figure, digital voices △ and B are digital signals sampled at 3) (tlz) and are samples and held for 125 μs.A multiplexing circuit 2 converts these digital voices A and B into time-division multiplexed voice signals. This signal is output in synchronization with a clock having a frequency of 16KH7, which is twice the sampling frequency of 8KHz.

This time division multiplexed audio signal is converted to 16K by D/A converter 3.
D/A conversion is performed using the llz clock. Therefore, the multiplexed audio signal has higher frequency components than the digital audio A and B, so by passing this signal through an LPF 4 with a cutoff frequency of 4KIIz, harmonic components generated during multiplexing are removed. An analog audio waveform 5 obtained by mixing the digital audio A and B is extracted.

In this way, when mixing digital audio waveforms,
By time-division multiplexing of digital audio waveforms,
Noise is less likely to enter, there is no need to individually D/A convert multiple digital audio waveforms and pass them through the LPF 7-:, and the D/A converter 3 and LPF 4 can be configured with one each, making the device easier to use. can be made inexpensive and compact.

Further, as an application of the device, it is possible to realize an inexpensive system in which an alarm sound for the operator is sent from the same playback system while the synthesized sound is being played back.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, by multiplexing a plurality of digital audio waveforms and then performing D/A conversion, it is possible to reduce the cost and size of the device.
This has the effect that it is possible to provide an audio reproduction circuit that is less susceptible to noise.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a time chart of the multiplexing circuit shown in FIG. 1, and FIG. 3 is a block diagram showing a conventional example. Explanation of symbols of main parts 2... Multiplexing circuit 3... D/A converter

Claims (1)

[Claims] An audio reproduction circuit that mixes and reproduces a plurality of pieces of audio information, comprising multiplexing means for multiplexing each of the audio information as a digital signal, and reproducing the output of the multiplexing means into an analog signal. An audio playback circuit characterized by: